Ruthenium complexes of the formula A are known from WO 02/14376 A2 and are described as active, air-stable and recoverable metathesis catalysts. Further catalysts of this type which are described by the formulae B, C and D and have an even higher activity than A have become known (Angew. Chem. 2002, 114, No. 5, 832-834; Angew. Chem. 2002, 114, No. 13, 2509-2511; Angew. Chem. 2002, 114, No, 21. 4210-4212).
The improvement in the activity of B and C compared to A is attributed to steric and electronic effects of the substituents on the benzene ring, and in the case of D to a specific change in the aliphatic radical of the ether group of the ligand.

It has now surprisingly been found that a further increase in the activity of ruthenium catalysts of the formula A can be achieved, even compared to D, by introducing a keto group into the aliphatic radical of the ether group of the ligand.